What Is Ocular Toxoplasmosis?
Ocular toxoplasmosis is an inflammatory condition of the retina. It causes several eye complications like retinal detachment, glaucoma, and vision loss. The retina is that part of the eye that receives the sensory signals and sends images to the brain. It is primarily an inflammatory condition exhibiting alarming symptoms, especially in immunocompromised individuals. It presents diverse clinical manifestations.
What Causes Ocular Toxoplasmosis?
The primary causative organism responsible for ocular toxoplasmosis is toxoplasma gondii (t.gondii). It affects warm-blooded animals, including humans. It is responsible for infecting human beings. They are more prevalent in tropical regions.
Life Cycle of T.gondii
The eggs of toxoplasma are responsible for active infection in the host cells. The repeated destruction of the host cell followed by the reentry of eggs into the cell leads to the death of the tissue (necrosis).
What Are the Different Sources of Infection?
The parasite is transmitted to humans by several routes such as:
-
Accidental ingestion of the eggs of the parasite in feces of cats present in parks roads.
-
Improper washing and consumption of uncooked fruits and vegetables.
-
Ingestion of raw meat is also considered the leading cause of transmission.
-
To the growing fetus of a pregnant mother.
-
Transfusion of blood from seropositive patients.
How Does Ocular Toxoplasmosis Develop?
The exact mechanism by which the parasite causes infections in humans is unknown.
-
After ingestion, the eggs of the parasite are present inside the host cell in an inactive form. These eggs reach the eyes through the bloodstream.
-
Several factors like hormonal changes, diminished immunity, and age trigger activation of the eggs that are released from their cyst.
-
After their release, they induce an inflammatory reaction that manifests clinically.
What Are the Different Types of Ocular Toxoplasmosis?
The are two primary forms of ocular toxoplasmosis:
Congenital Toxoplasmosis - This form of ocular toxoplasmosis is present at birth. It was earlier considered to be the most common form. The infection is transmitted to the newborn from the mother. The most common manifestation of congenital ocular toxoplasmosis include:
-
It is defined as the inflammation of the retina and choroid (retino-choroiditis).
-
One or both eyes are small from birth (microphthalmia).
-
Wasting away of the optic nerve.
-
Opacification of the lens (cataract).
-
Strabismus (cross eyes).
-
It is a clinical presentation seen in the retina due to atrophy and hyperpigmentation of the macular lesion, giving a classic wagon-wheel appearance.
Acquired Toxoplasmosis - It mainly occurs in the second and fourth decades. It is now considered to be more common than the congenital form. Patients with acquired toxoplasmosis also exhibit fatigue, malaise, and inflammation of cervical lymph nodes. It mainly manifests as -
-
Altered vision with retinitis.
-
Inflammation of the anterior part of the middle layer of the eyewall (anterior uveitis).
-
Raised intraocular pressure.
What Are the Clinical Signs and Symptoms of Ocular Toxoplasmosis?
The best way to diagnose ocular toxoplasmosis is based on its clinical signs and symptoms. The classic features associated with ocular toxoplasmosis include:
-
Inflammation of the vitreous body. Inflammation of the vitreous is more intense near the lesion of active retinochoroiditis. It causes a bright white reflex when one shines the light of the indirect ophthalmoscope into the back of the eye, which is called the "headlight in the fog" appearance.
-
Retinochoroidal scar (formed after the atrophy of the active lesion).
-
Inflammation surrounding the blood vessel with arterial plaques known as Kyreiles plaques.
-
Inflammation of the optic nerve.
-
Multiple cysts in the macula (cystoid macular edema) are seen in cases having active lesions.
-
Atypical ocular toxoplasmosis is toxoplasmosis of the immunocompromised. It includes multifocal, bilateral, and diffuse retinal lesions in patients with severely reduced immunity, like AIDS (acquired immunodeficiency syndrome) patients and the elderly. There are distinct dense yellowish-white borders around the lesions seen in these patients.
What Are the Complications of Ocular Toxoplasmosis?
Ocular toxoplasmosis is mostly a self-limiting disease. However, in severe persistent and untreated cases, it may cause many complications such as -
-
Chronic inflammation of the iris and ciliary body of the eye.
-
Cataract (opacification of the eye lens).
-
Secondary glaucoma.
-
Degeneration of the cornea with fine calcium deposits in the subepithelial layer.
-
Detachment of the retina from blood vessels supplying it leads to oxygen deprivation.
-
Optic nerve damage.
-
Increased formation of blood vessels in the middle layer of the eye between sclera and retina (choroid) resulting in vision loss.
How to Diagnose Ocular Toxoplasmosis?
The diagnosis of toxoplasmosis of the eye is made by ophthalmic examination. Other diagnostic tests implemented for the diagnosis of toxoplasmosis include:
-
Serological Tests (Study of Blood) - Antibodies or immunoglobulins (IgG and IgM) against the toxoplasma species indicate an active or recent lesion. But these tests are no definitive diagnostic tests.
-
Definitive Tests - These tests include dye tests like (Sabin-Feldman), IFAT (indirect fluorescent antibody test), immunoblot, and ISAGA (immunoglobulin-M immunosorbent agglutination assay). These tests are expensive. Serological tests can give false-positive and false-negative results.
-
Goldman Witmer Test - It is an index that determines the intraocular antibodies produced in immunocompetent patients.
-
Polymerase Chain Reaction (PCR) - It is performed mainly in older patients, and samples are collected within one week. It has a lesser sensitivity than the Goldman Witmer test.
-
Imaging - The different imaging modalities to confirm the diagnosis of toxoplasmosis of the eye includes -
-
Autofluorescence Imaging - It helps assess the pigmentation of the retinal scar and monitor the effectiveness of the medication.
-
Ultrasonography - It detects the location of fluid leakage, retinal wall thickening, and retinal detachment despite the opacity.
What Are the Conditions Which Are Similar to Ocular Toxoplasmosis?
-
Serpiginous choroiditis is a rare recurrent disorder characterized by irregular lesions involving the retina and capillaries of the choroid.
-
Necrotizing retinitis is an inflammatory and infectious disease of the retina characterized by its death.
-
White dot syndromes are spontaneously occurring inflammatory conditions of the retina and choroid.
How Can We Treat Ocular Toxoplasmosis?
Management of ocular toxoplasmosis includes both medical and surgical approaches. It is a self-limiting disease. Small lesions or asymptomatic cases in immunocompetent patients do not require any treatment. The primary rationale behind the treatment is to decrease the parasitic count and reduce the damage occurring in the eye.
-
Medical Management of Toxoplasmosis:
The most commonly used treatment regimen includes antiparasitic and corticosteroid drugs.
1. Antimicrobials:
-
Pyrimethamine with Folinic Acid is the classical drug followed for active toxoplasmosis cases. Pyrimethamine is linked to gastrointestinal, skin, and defects.
-
Trimethoprim and Sulfamethoxazole with corticosteroid combination is a well-tolerated drug regimen. Trimethoprim and Sulfamethoxazole combination is given prophylactically to decrease the recurrence rate and duration of the infection. It causes only mild gastrointestinal side effects with rashes.
-
Clindamycin as a quadruple therapy is administered orally or intravenously (to avoid systemic complications). It is used to treat the active lesions of the retina. Recurrent mild cases do not require any treatment in pregnant females. Intravitreal Clindamycin is the treatment of choice for mothers.
2. Oral steroids:
-
It is used in active cases to reduce inflammation and prevent further hardening of the lesion. It is avoided in immunocompromised patients to prevent any other opportunistic disease.
Surgical Management:
-
Ocular surgeries are performed only after reducing the parasite burden.
-
Vitreoretinal surgeries are indicated for the correction of retinal detachment, vitreous opacities, and refractory vitritis.
-
Cataract surgery with an intraocular lens is indicated if the lens is severely opacified after the resolution of the inflammation.
Can We Prevent Ocular Toxoplasmosis?
The onset of the disease can be prevented by following a few simple preventive measures. These measures include:
-
Consumption of only cooked food and pasteurized milk is advised.
-
People with compromised immunity, like acquired immunodeficiency syndrome (AIDS) and pregnant females, should be extra vigilant.
-
Pet owners should get their pets vaccinated regularly.
-
Transfusion of blood is recommended only after checking for seronegativity for toxoplasma species.
What Is the Prognosis of Ocular Toxoplasmosis?
The prognosis of the disease depends upon the site involved and the host's immunity.
-
Many immune-competent patients are primarily asymptomatic or suffer mild symptoms. Patients with compromised immunity are severely affected.
-
Severe damage to the macula (the part of the eye responsible for sharp central vision) and optic disc (entry point of the optic nerve) might lead to permanent vision loss.
What Is the Recurrence Rate and Severity of Ocular Toxoplasmosis?
The recurrence rate of the disease is more in the first year after getting infected than in the subsequent years. People above sixty are less likely to get the disease again than youngsters. The severity of the disease depends mainly on an individual's immunity and hormonal imbalance.
Conclusion
Ocular toxoplasmosis is primarily an infectious parasitic disease affecting the eye. Most of the immunocompetent are asymptomatic. Accurate diagnosis and proper management will lead to the complete remission of the disease.
